The present invention relates to the field of magnetic separation of particles in a solution. More specifically, the present invention relates to an arrangement of magnets for separating particles in a solution.
Biological laboratories often require a technique to separate particles in a solution. Target particles, such as proteins and the like, are separated from a solution by a technique known as magnetic separation.
In general, the case of molecular biological magnetic separation of biological particles, such as target proteins, involves coating small paramagnetic materials, such as micro-beads ranging in size from a few hundred nanometers to tens of micrometers, with a chemical-specific substance that is known to chemically bond with the target proteins. The coated micro-beads are introduced into a well containing a solution of the target proteins and unwanted biological molecules. The target proteins chemically bond to the coating of the micro-beads. Magnets are placed close enough to the well to apply magnetic fields on the well and the solution.
The paramagnetic micro-beads, including the target proteins chemically bonded to the coating of the micro-beads, are attracted to the magnets in accord with the direction of the magnetic fields the magnets generate. Placement of the magnets determines where the micro-beads with the target proteins will collect, i.e., if the magnets are placed along the side of the well, the micro-beads will collect to the side wall of the well. Once the micro-beads have been collected to the desired location, the well is rinsed, removing the solution. The collected micro-beads with the target proteins chemically bonded to the coating of the micro-beads remain in the well as long as the magnetic fields are continually applied.
Once the well has been rinsed, a xe2x80x9ccleanxe2x80x9d solution, without unwanted particles, is placed into the well. A chemical is introduced into the xe2x80x9ccleanxe2x80x9d solution to break the chemical bonds of the target proteins and the coating of the micro-beads, resulting in a well with isolated target proteins. Additionally, the micro-beads may be removed by no longer applying the magnetic fields to the well.
Molecular biological magnetic separation is well known, and until relatively recently, this process was performed using large tubes of fluids (15-50 ml tubes) and micro-beads. Recent molecular magnetic separation techniques typically involve the use of 96-well micro-plates, that is, a tray having 96 wells, arranged in and 8xc3x9712 matrix, with each well capable of holding 250-500 micro-liter (xcexcl) of liquid. A variety of placement methods for magnets to apply the desired magnetic fields can be employed on these micro-plates. One method is to place small magnets, having predetermined magnetic fields, between micro-plate receiving orifices, so that the micro-beads collect along the walls of the wells as described by Li, et al., U.S. Pat. No. 4,988,618. Another method is to place an apparatus with magnetic pins into the wells with the micro-beads collecting on the pins as described by Ekenberg, et. al., U.S. Pat. No. 5,567,326. Another method is to have a base for a micro-plate with cylindrical magnets positioned for insertion from the base of the micro-plate into the spaces between the wells of the micro-plate with the micro-beads collecting along the walls of the wells as described by Yu, U.S. Pat. No. 5,779,907.
As molecular magnetic separation techniques advance, the number of wells increase, and therefore, in high throughput applications, typically in automated systems, 384-well micro-plates and 1536-well micro-plates are utilized. Each 384-well micro-plate is arranged as 16xc3x9724 wells, and each 1536-well micro-plate is arranged as 32xc3x9748 wells effectively increasing the volume of the 96-well micro-plates by 4 and 16 times respectively.
The spaces between the individual wells in the 384-well and 1536-well micro-plates are relatively very small; making the magnetic separation methods of Li, Ekenberg, and Yi difficult, if not impracticable. However, magnets are still required to separate the target particles from the solution for the high throughput 384-well and 1536-well micro-plates. Also, due to the increased density of the wells, if magnetic fields are applied from areas outside of the micro-plate, the separation of particles becomes inconsistent across the micro-plates because some of the wells experience a larger magnetic field than other wells.
Disclosed is an improved arrangement of magnets for consistent magnetic separation of particles across a container, such as in the case of molecular biological magnetic separation of biological particles of the type described above. Due to the arrangement of the magnets, in particular, poles of the magnets, particles in a solution in the container are magnetically separated consistently across the container. The arrangement of the magnets allow for magnetic separation within a wide range of containers, such as micro-plates with increasing density of wells.